There are new results released based on data gathered by the WISE mission that shows that brown dwarfs are not as common as previously thought. The results show that brown dwarfs in the solar neighborhood are only about 1/6 as common as normal stars. This is based on preliminary data, but it is thought that future data will bring the total ratio to no more than 1:4, far less than the 1:1 that was previously expected.

Perhaps this should be taken into account for the future development of SpaceEngine?

If so, space bodies distribution have a strange gap. Nubmer of stars grows exponentially as reducing of their mass: entire galaxy have only few O3 stars, billions of Sun-like stars, and 100-200 billions of red dwarfs. Brown dwarfs continue this list - they have a mass intermediate between red dwarfs and giant planets. We may expect that galaxy have trillions of them... Modern data says that almost all stars have at least one planet and there are many planemo (planets without suns) floating in interstellar space - 2x times much than stars. So they may contimue distribution curve of stars, but brown dwarfs make a gap in it...

I agree, it is strange, if it is true. I had long expected (as many astronomers had) that there should be at least as many brown dwarfs as there are M dwarfs, if not many more, and that there should be also many planet-mass objects in interstellar space, which observations support.

I think I read somewhere that there is possibly a gap in the mass-distribution of white dwarfs? Or perhaps it was a different type of star/degenerate/substellar object, but I think white dwarf. It was in some published paper I read one time when doing research for something, I forget what it was now. But I wonder - if such a gap exists - if it is due to observational bias or if there really are such curious gaps.

That is true, but there is a time delay between one and the other (for example, low mass stars would take longer to leave the main sequence than the amount of time that the universe has existed). So there should be a "cliff", a sudden drop in white dwarf mass below a certain threshold (that is unrelated to what I was talking about in my previous post however). But because of this time delay, if there was any mass-gap in stellar populations in the early universe, then that could be detectable in the white dwarf population. So it is possible to have a gap in a degenerate population without having an obvious gap in the current stellar population.

That said, aside from that one paper that I may or may not have read, I have no reason to think that any such gap exists.

Might the gap perhaps be caused because a gas cloud small enough to form into a brown dwarf in the same way stars get formed just isn't massive enough to contract well, making it relatively less likely a brown dwarf is formed, while brown dwarfs formed like planets are less likely to form because there needs to be an awful lot of mass left around a star to form one? It's just a wild guess.

Perhaps most brown dwarfs just emit so little light that they're too hard to detect.

They emit in infrared light, which is what this mission was searching in. It found plenty of brown dwarfs, including some that were of very low luminosity, so it has proven itself quite capable of detecting them. It just discovered far fewer than expected.

Has there been any news on the matter of the hypothetical brown dwarfs/dwarf stars/planets of Nemesis or Tyche?

If Nemesis had existed, WISE would have found it. So it has now been pretty conclusively disproven. We have also accounted for all major sources of gravity in the Solar system, so there are no major planets that are undiscovered. Mercury-Neptune is it.